Permanent magnets composed of cobalt and rare earth alloys have come into prominence in recent years because of the very high energy product of such magnets and because they can maintain a high and constant magnetic flux in the absence of an exciting magnetic field or electrical current to bring about such a field.
In order to prepare cobalt-rare earth magnets having the most desirable properties, it is necessary to exercise great care in the production of such magnets. Benz U.S. Pat. Nos. 3,655,463, 3,655,464, 3,695,945, and Benz and Martin U.S. Pat. No. 3,684,593 disclose and claim processes for making sintered cobalt-rare earth magnets.
Rare earth metals and alloys are very active chemically, particularly at elevated temperatures, and for this reason the four patents cited above stress the importance of inert atmospheres such as purified argon during production. It has long been known that rare earths will readily react with nitrogen and will also react with hydrogen to form hydrides. For this reason care has been taken to bar hydrogen from contact with the rare earth material during sintering and other high-temperature processing steps.